The present invention relates generally to high-pressure fuel injection valves or injectors for internal combustion engines, and, more specifically, to an injection valve that is directly controllable by a position actuating magnetostrictive material and that includes a passive hydraulic link.
Direct injection of a gaseous fuel into the combustion chamber of an internal combustion engine is desirable for several reasons. For example, direct injection allows charge stratification, eliminating throttling losses associated with homogeneous charge engines. Additionally, with direct injection late in the compression stroke, a high-compression ratio can be maintained, maintaining the efficiency of conventional diesel engines. Further, when the fuel that is directly injected comprises natural gas, propane, or hydrogen, the emissions of NOx and particulate matter (PM) are significantly reduced. The directly injected gaseous fuel can be ignited with a glow plug, with a spark plug, with pilot diesel fuel, or with any other energy source. The gaseous fuel should be injected at high pressure to overcome the combustion chamber pressure, which is high at the end of the compression stroke. Preferably, the injection pressure is high enough to promote good mixing between the injected fuel and the combustion chamber air.
Direct injection at high pressures presents several challenges. The use of high-pressure fuels for direct injection results in high fuel pressures existing within the injection valve or injector. As a result, when closed, the injection valve should typically be strongly seated to avoid leakage of the fuel into the combustion chamber between injection events. When the valve is a needle valve, the valve is seated when the sealing surfaces of the movable valve needle and the valve seat are in fluid-tight contact with each other. The valve seat is generally part of the valve housing or body.
Moreover, compared to low-pressure systems, higher forces are needed to open the injection valve since the valve should be strongly seated to remain sealed when the valve tip is exposed to the high pressures generated in the combustion chamber. High closing forces are also involved since the needle of a fuel injection valve for a high-pressure system should overcome the high forces generated by the exiting pressurized fuel when the needle is in the open position.
Additionally, there is only a small window of time during which the fuel can be injected. For example, at 4500 revolutions per minute (RPM), at full load, all of the fuel is preferably injected in less than 2-3 milliseconds.
Co-owned U.S. Pat. No. 6,298,829 discloses an injection valve that can achieve the performance to inject a gaseous fuel through injection events having a duration of less than 2-3 milliseconds. A preferred embodiment of the injection valve disclosed in the ""130 application comprises a tubular magnetostrictive actuator assembly with a valve needle that extends axially through the center of the actuator assembly. The actuator assembly comprises a tubular magnetostrictive member that expands in length when it is actuated by subjecting it to a magnetic field. The magnetic field is generated, for example by directing an electric current through an electric coil disposed in an annular space around the tubular magnetostrictive member.
An advantage of this arrangement is that a more compact length is achieved since the tubular actuator assembly overlaps with the valve needle. However, a concern with respect to this arrangement is that the valve needle extending through the actuator assembly may cause interference with the magnetic field and some of the magnetic flux may be drained from the magnetostrictive member and conducted through the valve needle. Accordingly, for injection valves employing such an arrangement, there is a need to ensure that the valve needle does not interfere with the operation of the actuator assembly.
An injection valve injects fuel into a combustion chamber of an internal combustion engine. The injection valve comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port;
a nozzle comprising a valve seat and at least one nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) an actuator assembly disposed within the valve housing, the actuator assembly comprising a magnetostrictive member actuatable by imposition of a magnetic field to expand in length to provide a valve opening force;
(c) a plurality of portions joined together to form a unitary valve needle disposed within the valve housing and extending through the actuator assembly, the unitary valve needle comprising:
a shaft portion formed from a non-ferromagnetic material, the shaft portion extending through the magnetostrictive actuator assembly;
a valve needle tip having sufficient durability to contact and seal the valve seat over multiple opening and closing cycles; and
a member through which the valve opening force is transferred from the tubular actuator assembly to the unitary valve needle,
wherein the unitary valve needle is movable between a closed position at which the valve needle tip contacts the valve seat to fluidly seal the interior chamber from the nozzle orifice, and an open position at which the valve needle tip is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice; and
(d) a needle biasing mechanism associated with the valve needle, the needle biasing mechanism applying a closing force to the valve needle for biasing the valve needle in the closed position.
In a preferred injection valve, the actuator assembly and the magnetostrictive member are tubular. The valve needle tip is preferably formed from a material having through-hardness greater than that of the non-ferromagnetic material. The preferred needle biasing mechanism is a spring, most preferably at least one disc spring.
In the above-described arrangement, the actuator assembly is disposed in an annular space that surrounds a portion of the valve needle. This is a preferred arrangement because it allows for a compact design. The actuator assembly is typically elongated and has a length that is determined by the desired lift, which in turn determines the length of the magnetostrictive member. When a magnetostrictive actuator is actuated, a magnetic field is applied to the magnetostrictive member to cause it to expand in length. Longer magnetostrictive members are able to expand by greater amounts, resulting in greater lift when used in an injection valve application.
Conventional devices with similar arrangements (that is, a solid member extending through a tubular magnetostrictive member) employ a non-ferromagnetic member to avoid interfering with the magnetic field. In the field of magnetostrictive materials, it is generally believed that employing a ferromagnetic material for the valve needle will cause leakage of magnetic flux, which may in turn compromise performance since all flux is intended to pass through the tubular magnetostrictive member and the flux paths provided by conventional poles and flux tubes. Consistent with such beliefs, conventional devices with similar arrangements have employed non-ferromagnetic materials such as, for example, austenitic stainless steel, titanium and ceramics.
A disadvantage of using a non-ferromagnetic material for the present application, however, is that the valve tip is subjected to high frequency impact loads caused whenever the valve tip is seated against the valve seat. Compared to ferromagnetic materials, non-ferromagnetic materials such as titanium and austenitic stainless steel generally cannot be hardened to match the durability of ferromagnetic materials. Past approaches to solving some of these disadvantages have included coating the non-ferromagnetic material to improve its durability, but coatings are generally more suited to components that are subjected to sliding movements rather than impact loads.
The ferromagnetic material for the valve needle tip is preferably a suitable tool steel. For example, a tool steel such as H type or M type is a preferred material for the valve needle tip. Examples of a suitable non-ferromagnetic material for the shaft portion are members formed from titanium alloys, austenitic stainless steels and ceramics. Accordingly, the composite needle is preferably made from at least two pieces made from different materials that are joined together to provide a unitary composite needle. That is, the composite needle preferably comprises a non-ferromagnetic shaft piece and a ferromagnetic valve needle tip. Those skilled in the art will recognize that other embodiments are possible wherein the composite needle comprises three or more pieces joined together.
The injection valve preferably further comprises a hydraulic link assembly comprising a passive hydraulic link having a hydraulic fluid thickness through which the opening and closing forces are transmitted. The hydraulic fluid acts substantially as a solid with the thickness being substantially constant while the actuator assembly is actuated and wherein the thickness of the hydraulic link is adjustable while the actuator is not activated in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift upon actuation of the actuator assembly.
In a preferred embodiment, the thickness of the hydraulic link is auto-adjustable in response to changes in the dimensional relationship caused by differential thermal expansion, variations in manufactured dimensions within design tolerances, and/or wear to components of the injection valve. The hydraulic link assembly preferably comprises a fluidly sealed hydraulic cylinder, with a piston and hydraulic fluid disposed within the hydraulic cylinder. The piston may be an integral part of the composite valve needle. The piston may be formed from a different material than the valve shaft portion. For example, for durability, the piston is preferably formed from a material that is hardenable to a greater through-hardness than the shaft portion, which is made from a non-ferromagnetic material. For example, the piston may be made from a material such as stainless steel, but a harder material such as tool steel is preferred. Because there is a very small clearance gap between the piston and the hydraulic cylinder, it is also desirable for the piston to be made from a material that can be readily machined to high tolerances. For example, chromium-molybdenum steel alloys such as AISI 4140 specification steel are suitable materials for the piston.
The actuator assembly preferably comprises an electric coil disposed around the magnetostrictive member and a flux tube disposed around the electric coil. In preferred arrangements, the actuator assembly may be disposed within the interior chamber of the injection valve. One end of the tubular actuator assembly may be held in a fixed position in relation to the valve housing by a pole that supports the magnetostrictive member. The pole is attached to the valve housing to prevent movement of the supported end of the magnetostrictive member when the actuator assembly is actuated. In one embodiment, the flux tube and/or the pole associated with the valve housing are integral parts of the valve housing and/or the magnetostrictive member. In this embodiment the valve housing is formed from a magnetically permeable material, such as common carbon steel and the valve housing advantageously also acts as the flux tube, obviating the need for a separate component.
In a preferred embodiment, the injection valve comprises an inlet port and nozzle orifices arranged substantially at opposite ends of the injection valve. Fluid passages extend through or between the actuator and hydraulic link assemblies and the valve housing to allow fuel to flow from the inlet port to the nozzle orifices. The flow of fuel through such fluid passages cools the actuator and hydraulic link assemblies. Such fluid passages may be formed by longitudinally-oriented grooves in the surfaces of components of the actuator assembly and the hydraulic cylinder and/or longitudinally-oriented grooves in the inner wall of the-valve housing. Providing port openings through components of the actuator, the hydraulic link assemblies and the valve housing may also form such fluid passages.
The actuator assembly is controllable to control the desired lift between 10 and 100 percent of maximum lift. That is, the control pulse directed to the actuator assembly can be modulated to provide full or partial lift, as desired. The control pulse is a modulated electric current directed to an electric coil that produces a magnetic field.
The present injection valve is particularly suited for injecting a gaseous fuel because the ability to modulate the movement of the valve needle may be beneficially used to slow down the closing action of the valve needle to reduce impact upon closing. When a liquid fuel is injected, the closing impact is dampened by the displacement of the thin liquid fuel layer, which is considerably denser than gaseous fuels. When the fuel is a gaseous fuel, it can be injected into the combustion chamber at a pressure greater than about 2000 psi (about 13.8 MPa).
A magnetostrictive material that is suitable for use in the present injection valve comprises a material known as ETREMA Terfenol-D(copyright) magnetostrictive alloy that is available from Etrema Products Inc. ETREMA Terfenol-D(copyright) magnetostrictive alloy is a metal alloy composed of the elements terbium, dysprosium and iron.
In a preferred embodiment, the valve needle, actuated by a magnetostrictive assembly, is controllable to move between the closed and open positions in less than about 250 microseconds.
To improve the range of valve lift for an actuator comprising a magnetostrictive member with a given length, a compressive force may be applied to the magnetostrictive member. The net displacement may be increased per respective unit of applied magnetic field by pre-loading the magnetostrictive member. Accordingly, a compression spring member may be employed for applying a compressive force to pre-load the magnetostrictive member. In a preferred embodiment, the compression spring member comprises at least one disc spring (also known as a Belleville spring or Belleville washer).
The injection valve housing may comprise a plurality of parts that are joined with each other to provide a fluidly sealed body. For example, the valve housing may comprise a hollow main housing with a removable valve cap that allows access to the valve components disposed within the main housing. The valve housing may further comprise a separate valve tip so that it is replaceable when worn. In addition, the valve tip may be designed so that it is the only portion of the valve body that is directly exposed to the interior of the combustion chamber. In this case, the valve tip may be formed from a material that will provide greater durability when directly exposed to the conditions that might be expected within a combustion chamber.
While the hydraulic link is designed to compensate for changes in the dimensional relationships between valve components, including changes caused by differential thermal expansion, the demands placed upon the hydraulic link may be reduced by the selection of materials for the valve components that have similar thermal expansion coefficients.
A preferred fuel injection valve for an internal combustion engine comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port;
a nozzle comprising a valve seat and a nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) an actuator assembly disposed within the valve housing, the actuator assembly comprising:
a tubular magnetostrictive member actuatable to expand in the direction of an applied magnetic field to thereby apply an opening force that is stronger than a closing force;
an electrical coil disposed around the magnetostrictive member;
a flux tube disposed around the electrical coil; and
a support for the actuator assembly that acts as a pole and provides a fixed position for one end of the magnetostrictive member relative to the valve housing;
(c) a plurality of portions joined together to form a unitary valve needle disposed within the valve housing, the unitary valve needle comprising:
a shaft portion formed from a non-ferromagnetic material, the shaft portion extending through the tubular magnetostrictive actuator assembly;
a valve needle tip formed from a material having a through-hardness greater than that of the non-ferromagnetic material for contacting the valve seat; and
an integral piston member through which the valve opening force is transferred from the actuator assembly to the unitary valve needle;
wherein the unitary valve needle is movable between a closed position at which the valve needle tip contacts the valve seat to fluidly seal the interior chamber from the nozzle orifice and an open position at which the valve needle tip is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice;
(d) a needle spring associated with the valve needle, wherein the needle spring is compressible to apply the closing force to the valve needle for biasing the valve needle in the closed position; and
(e) a passive hydraulic link assembly comprising a sealed hydraulic cylinder disposed about the piston member, a hydraulic fluid disposed within the hydraulic cylinder, wherein the opening and closing forces applied to the valve needle are transmitted through a thickness of the hydraulic fluid whereby the hydraulic fluid acts as a hydraulic link and the thickness is automatically adjustable in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift when the actuator assembly is actuated.
A composite valve needle can have advantages over a single piece valve needle since a material can be selected for the valve tip that has improved durability characteristics, a material can be selected for the shaft piece that is non-ferromagnetic, and a material can be selected for an integral piston that is durable and easy to machine to high tolerances. In addition, since non-ferromagnetic materials like titanium are lighter than equivalent ferromagnetic materials like tool steel, the shaft piece material can also be selected to reduce the overall mass of the composite needle. These and other advantages are provided by a directly actuated injector as described below.